In recent years, more and more portable electronic devices such as mobile phones and PDAs (Personal Digital Assistances) are having a panel switch using a movable contact element on the operation unit. A conventional movable contact element and a panel switch using it will be described as follows with reference to drawings.
FIG. 5 is a cross sectional view of the movable contact element, FIG. 6 is an exploded perspective view of the movable contact element, FIG. 7 is a view showing application of adhesive to the area of a base sheet that corresponds to a movable contact point as a component of the movable contact element, and FIG. 8 is a cross sectional view of the conventional panel switch using the movable contact element.
In FIG. 5, movable contact element 50 includes movable contact point 1. Movable contact point 1, which is made of an elastic metal thin film that is circular when seen from above, has a convexly domed top and an open bottom. Note that although FIG. 5 shows only one movable contact point 1 for convenience of explanation, typical touch panels have a large number of movable contact points 1. Each movable contact point 1 includes domed part 1A with throughhole 1B at its center.
Base sheet 2 is made of an insulating film such as PET (Polyethylene terephthalate). Each movable contact point 1 is in position with the outer surface of domed part 1A fixedly bonded to the bottom surface of base sheet 2 by adhesive 3 applied on the bottom surface of base sheet 2.
FIG. 6 is an exploded perspective view of movable contact element 50. Movable contact element 50 includes movable contact points 1 each having domed part 1A and throughhole 1B. As mentioned above, different portable electronic devices have different numbers of movable contact points 1. Movable contact element 50 includes base sheet 2 and adhesive 3 having peripheral part 3B.
FIG. 7 shows the positional relationship between base sheet 2 and adhesive 3 applied on base sheet 2 in order to fix movable contact point 1. The area with adhesive 3 thereon is shaded for clarity.
As shown in FIG. 7, adhesive 3 for fixing movable contact point 1 is applied in the shapes of circular ring part 3A and peripheral part 3B surrounding it, which are separate from each other. In other words, peripheral part 3B is formed outside circular ring part 3A with a prescribed spacing therebetween. Peripheral parts 3B are formed nearly on the entire bottom surface of base sheet 2.
FIG. 8 is a cross sectional view of the panel switch using the conventional movable contact element. Conventional panel switch 80 shown in FIG. 8 has movable contact element 50 shown in FIG. 5 including movable contact point 1, base sheet 2 and adhesive 3.
Panel switch 80 further includes fixed contact point 4 having a pair of outer fixed contact point 4A and central fixed contact point 4B. Fixed contact point 4 is formed on one main surface 5a of wiring board 5.
Movable contact point 1 and fixed contact point 4 are arranged in a predetermined positional relationship.
More specifically, circumferential bottom edge 1C of movable contact point 1 is placed on outer fixed contact point 4A in such a manner that throughhole 1B formed in the center of domed part 1A is substantially vertically aligned with the center of central fixed contact point 4B. Outer fixed contact point 4A and the bottom surface of base sheet 2 are fixedly bonded to each other by peripheral part 3B of adhesive 3.
Outer fixed contact point 4A becomes electrically continuous with the corresponding movable contact point 1, and the inner surface of domed part 1A of movable contact point 1 is opposed to the corresponding central fixed contact point 4B with a prescribed spacing therebetween.
This structure allows movable contact points 1 formed under the bottom surface of base sheet 2 to form single switches, thereby making up a panel switch as a whole. Above base sheet 2 are formed manual operation buttons 6 made of, e.g. rubber via which any of movable contact points 1 can be pressed.
In movable contact element 50 mentioned above, the bottom surface of base sheet 2 is generally covered with a protection sheet made of, e.g. an insulating film in order to protect movable contact points 1 and adhesives 3 from dust and the like during transportation and storage. The protection sheet is removed before base sheet 2 is bonded to wiring board 5.
Each single switch of the panel switch operates as follows. When the user presses manual operation button 6 of an electronic device, domed part 1A of movable contact point 1 below manual operation button 6 is pressed downward via base sheet 2. Then, domed part 1A is turned upside down with a sense of moderation, and the inner surface of domed part 1A comes into contact with central fixed contact point 4B. As a result, outer fixed contact point 4A and central fixed contact point 4B become electrically continuous with each other. Throughhole 1B of movable contact point 1 is pressed locally at its end against central fixed contact point 4B, thus enabling the switch to be in a stable ON state.
When the user releases the pressing force, the inner surface of domed part 1A leaves central fixed contact point 4B so as to restore domed part 1A to the original convex shape with a sense of moderation, thereby pushing back manual operation button 6 upward. As a result, the switch returns to the OFF state as shown in FIG. 8 in which outer fixed contact point 4A and central fixed contact point 4B are electrically independent of each other.
Prior art documents related to the invention of this application include Japanese Patent Unexamined Publications No.H10-188728 and No.2002-216582.
In these conventional movable contact elements and panel switch using them, for the user to have excellent operation feeling in a single switch, it is necessary to press the center of domed part 1A of movable contact point 1 by pressing manual operation button 6 formed on the electronic device side. However, when the panel switch is integrated into various electronic devices, variation in production processes and workability causes a slight misalignment between manual operation button 6 and the center of movable contact point 1. As a result, the electronic devices fail to provide the user with a predetermined level of operation feeling.
FIG. 9 shows another conventional panel switch to overcome these conventional problems. This panel switch is provided with pressing lug 8 which is fixedly bonded to the top surface of base sheet 2 in the center of domed part 1A of movable contact point 1. Providing pressing lug 8 enables pressing the center of movable contact point 1, even if manual operation button 6 is misaligned from the center of movable contact point 1 during production or integration process.
This structure provides the user with comparatively excellent operation feeling; however, fixedly bonding pressing lug 8 in a stable manner to base sheet 2 requires high-precision control of positioning pressing lug 8 during production and integration processes.